Acrylic copolymer elastomer and vulcanizable composition containing same

ABSTRACT

There are provided an acrylic copolymer elastomer containing an acrylic acid polyalkylene glycol ester as a constituent, and a vulcanizable composition comprising said elastomer and a vulcanizing agent, which composition gives a vulcanizate excellent in cold resistance, heat resistance and oil resistance. The acrylic copolymer elastomer is obtained by copolymerizing 
     (a) 45 to 89.9% by weight of a monomer represented by the formula ##STR1## wherein R 1  denotes an alkyl group having 1 to 8 carbon atoms,  and/or a monomer represented by the formula ##STR2## wherein R 2  denotes an alkylene group having 1 to 8 carbon atoms, and R 3  denotes an alkyl group having 1 to 8 carbon atoms, 
     (b) 10 to 45% by weight of a monomer represented by the formula ##STR3## wherein R 4  denotes a hydrogen atom or a methyl group, R 5  denotes a hydrocarbon group having 1 to 8 carbon atoms, m is an integer of 2 to 10, and n is an integer of 2 to 3, 
     (c) 0.1 to 10% by weight of a crosslinkable monomer, and 
     (d) 0 to 30% by weight of a monoethylenically unsaturated monomer copolymerizable with components (a), (b) and (c).

This invention relates to an acrylic polymer elastomer and a vulcanizable composition containing same. More specifically, this invention relates to an acrylic copolymer elastomer containing an acrylic acid polyalkylene glycol ester as a constituent and a vulcanizable composition comprising said elastomer and a vulcanizing agent, which composition gives a vulcanizate having oil resistance, heat resistance and cold resistance and suitable for use as an industrial material.

Acrylic elastomers are polymer elastomers composed mainly of acrylic acid esters and are generally known as rubbers excellent in heat resistance, oil resistance and ozone resistance. They are used as molding materials of oil seals, O-rings, packings, and the like.

In recent years, with higher performance of automobiles, levels of heat resistance, oil resistance and cold resistance of the existing rubber materials cannot meet the required performance, and development of rubbers having still higher performance has been demanded.

In order to improve the properties of the rubbers, principally the monomer composition, the amounts and the types of ingredients, and the like have been changed, but it has been impossible to satisfy all the requirements of heat resistance, oil resistance and cold resistance.

For instance, as a method to improve cold resistance without impairing heat resistance and oil resistance, there is a method in which ethyl acrylate is copolymerized with a certain (meth)acrylic acid ester (Japanese Laid-Open Patent Application (Kokai) Nos. 264612/1988, 123809/1989, 132611/1989, 135811/1989, 299808/1989 and 22313/1990). In this method, however, cold resistance does not well balance with oil resistance, and there is a problem with compression set.

It is an object of this invention to remedy these defects associated with the prior art.

The present inventors have made assiduous studies to achieve the above object, and consequently have found that an acrylic polymer elastomer containing a certain acrylic ester is improved in cold resistance without impairing good heat resistance and oil resistance inherent therein and is excellent in balance between cold resistance and oil resistance.

Thus, in accordance with this invention, there are provided [I] an acrylic copolymer elastomer obtained by copolymerizing

(a) 45 to 89.9% by weight of a monomer represented by the formula ##STR4## wherein R¹ denotes an alkyl group having 1 to 8 carbon atoms, and/or a monomer represented by the formula ##STR5## wherein R² denotes an alkylene group having 1 to 8 carbon atoms, and R³ denotes an alkyl group having 1 to 8 carbon atoms,

(b) 10 to 45% by weight of a monomer represented by the formula ##STR6## wherein R⁴ denotes a hydrogen atom or a methyl group, R⁵ denotes a hydrocarbon group having 1 to 8 carbon atoms, m is an integer of 2 to 10, and n is an integer of 2 to 3,

(c) 0.1 to 10% by weight of a crosslinkable monomer, and

(d) 0 to 30% by weight of a monoethylenically unsaturated monomer copolymerizable with components (a), (b) and (c), said elastomer having Mooney viscosity [ML₁₊₄, 100° C.] of 10 to 100, preferably 15 to 70, and

[II] an acrylic copolymer elastomer vulcanizable composition comprising said elastomer, a vulcanizing agent and a vulcanizing agent auxiliary.

Among the monomers as component (a) used in this invention, the monomer represented by formula (1) is an alkyl acrylate having 1 to 8 carbon atoms, preferably 2 to 4 carbon atoms. Examples of said monomer are methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, cyclohexyl acrylate and octyl acrylate.

The monomer represented by formula (2) is an alkoxyalkyl acrylate containing an alkoxy group having 1 to 8 carbon atoms. Examples of said monomer are methoxymethyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate and butoxyethyl acrylate.

The amount of the alkyl acrylate or the alkoxyalkyl acrylate is 45 to 89.9% by weight, preferably 60 to 89.9% by weight based on the total weight of the monomer units. When the alkyl acrylate and the alkoxyalkyl acrylate are conjointly used, it is advisable that the amount of the alkoxyalkyl acrylate is 20 to 50% by weight.

Examples of the monomer as component (b), i.e., the monomer represented by formula (3) used in this invention are ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, methoxyoctaethylene glycol (meth)acrylate, methoxytetraethylene glycol (meth)acrylate, and methoxynonaethylene glycol (meth)acrylate. Especially preferable are those having 2 to 4 alkylene glycol units.

The amount of said monomer is 10 to 45% by weight, preferably 10 to 35% by weights based on the total weight of the monomer units. When it is less than 10% by weight, an effect of improvement in cold resistance is not provided. When it is more than 40% by weight, heat resistance and tensile strength decrease.

Examples of the crosslinkable monomer as component (c) in this invention are an active chlorine-containing unsaturated monomer, an epoxy group-containing monomer, a carboxyl group-containing monomer and a diene monomer.

Examples of the active chlorine-containing unsaturated monomer are vinyl chloroacetate, vinylbenzyl chloride, allyl chloroacetate, vinyl chlorobutyrate, 2-chloroethyl acrylate, 3-chloropropyl acrylate, 4-chlorobutyl acrylate, 2-chloroethyl methacrylate, 2-chloroethylvinyl ether, chloromethylvinyl ketone, 1-chloro-2-butenyl acrylate, 5-chloromethyl-2-norbornene, 5-chloroacetoxymethyl-2-norbornene, and 5-(alpha, beta-dichloropropionylmethyl)-2-norbornene.

Examples of the epoxy group-containing monomer are unsaturated glycidyl esters such as glycidyl acrylate, glycidyl methacrylate, diglycidyl itaconate, triglycidyl butenetricarboxylate, and glycidyl p-styrenecarboxylate; and unsaturated glycidyl ethers such as vinyl-glycidyl ether, allylglycidyl ether, and methacrylglycidyl ether.

Examples of the carboxyl group-containing monomer are unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumalic acid, 2-norbornene-5-carboxylic acid, maleic anhydride, and monomethyl maleate.

Examples of the diene monomer are butadiene, isoprene, cyclopentadiene, methylcyclopentadiene, ethylidene norbornene, and vinylidene norbornene.

These crosslinkable monomers can be used either singly or in combination. The amount of the crosslinkable monomer is 0.1 to 10% by weight, preferably 0.5 to 5% by weight based on the total weight of components (a), (b), (c) and (d). When said amount is less than 0.1% by weight, a sufficient crosslinking effect is not provided. When it exceeds 10% by weight, strength and elongation of the resulting acrylic copolymer elastomer vulcanizate notably decrease.

The monoethylenically unsaturated monomer as component (d) used in this invention is an optional component used if required to improve mechanical characteristics and oil resistance of the obtained acrylic copolymer rubber. Examples thereof are monovinyl monomers such as acrylonitrile, vinyl acetate, styrene, alpha-methylstyrene, acrylamide, vinyl chloride, and acrylic acid; and monovinylidene monomers such as methyl methacrylate, ethyl methacrylate, methacrylonitrile, and vinylidene chloride. The amount of the monoethylenically unsaturated monomer is 30% by weight or less based on the total weight of the monomer units.

The polymerization reaction can be preformed by polymerizing the monomer mixture through a known method such as emulsion polymerization, suspension polymerization, solution polymerization or bulk polymerization using an ordinary radical initiator. Said polymerization reaction may be conducted either batchwise or by adding one or more monomer components continuously or intermittently during the polymerization. The polymerization temperature is -10° C. to 100° C., preferably 2° to 80° C.

The vulcanizable composition of this invention is prepared by mixing the above obtained acrylic elastomer with a vulcanizing agent and a vulcanizing agent auxiliary.

A vulcanizing agent ordinarily used about the known acrylic elastomer containing the above crosslinkable monomer as a copolymerizable component is available as the vulcanizing agent. Examples of the vulcanizing agent are a combination of sulfur or a sulfur donor and an aliphatic acid metal soap or a combination of a dithiocarbamic acid salt or its derivative and trithiocyanuric acid in case of the elastomer containing the active chlorine group-containing unsaturated monomer as a copolymerizable component, a combination of ammonium benzoate, a dithiocarbamic acid salt, a combination of an isocyanuric acid and an onium salt in case of the elastomer containing the epoxy group-containing monomer as a copolymerizable component, a combination of a polyepoxy compound and an onium salt in case of the elastomer containing the carboxyl group-containing monomer as a copolymerizable component, and a sulfur vulcanizing agent or an organic peroxide vulcanizing agent in case of the elastomer containing the diene monomer as a copolymerizable component.

The acrylic copolymer elastomer of this invention can contain various additives commonly used in the rubber industry, such as a reinforcing agent, a filler, a plasticizer and an antioxidant.

The curing temperature of the elastomer is about 140° to 220° C. It is desirous that the vulcanizing temperature is about 160° to 200° C. Although the vulcanizing time depends on the vulcanizing temperature, it is generally 30 seconds to 20 minutes.

The vulcanizate made of the vulcanizable composition containing the acrylic polymer elastomer in this invention improves cold resistance that the ordinary acrylic copolymer rubber did not well satisfy, to a practical level, while maintaining good heat resistance, oil resistance and ozone resistance which are merits of the acrylic copolymer rubber; said vulcanizate has performance especially excellent in balance between oil resistance and cold resistance. Accordingly, the vulcanizable composition of this invention is useful in many fields requiring heat resistance, oil resistance, ozone resistance and cold resistance. Examples thereof are rubber parts such as gaskets, hoses, conveyor belts, packings, bearing seals, and oil seals.

The following Examples and Comparative Examples illustrate this invention more specifically. In said Examples, parts and percents are all by weight unless otherwise indicated.

EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 TO 3

A 2-liter separable flask was fitted with a thermometer, a stirrer, a nitrogen introducing tube and a pressure reducing device, and a mixture of monomers shown in Table 2 was polymerized in accordance with polymerization recipes (I) and (II) shown in Table 1. Namely, the components indicated in the polymerization recipe (I) were first charged in the flask, and pH of the mixture in the flask was then adjusted to 7. With stirring, the temperature inside the system was adjusted to 5° C., and deaeration and nitrogen purging were repeated to thoroughly remove oxygen in the system. Thereafter, the components indicated in the polymerization recipe (II) were added to start polymerization. The polymerization temperature was 5° C. and the reaction time was about 16 hours. Polymerization conversion was 94 to 98%. After the polymerization was over, the polymerization product was precipitated, well washed with water, and then dried for 24 hours with a vacuum dryer to afford a final acrylic polymer elastomer.

                  TABLE 1                                                          ______________________________________                                         (Polymerization recipe)                                                                               (g)                                                     ______________________________________                                         (I)  Water                   1000                                                   Sodium dodecylbenzenesulfonate                                                                         20                                                     Sodium naphthalenesulfonate                                                                            10                                                     Sodium sulfate          3                                                      Tetrasodium ethylenediaminetetraacetate                                                                0.2                                                    Sodium ferric ethylenediaminetetraacetate                                                              0.005                                                  Monomer mixture (Table 2)                                                                              1000                                              (II) Na.sub.2 S.sub.2 O.sub.4                                                                               0.2                                                    Sodium formaldehyde sulfoxylate                                                                        0.2                                                    p-Menthane hydroperoxide                                                                               0.1                                               ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________     (Monomer composition)                                                                     Acrylic copolymer                                                              elastomer                                                           Monomer composition                                                                       A    B    C    D    E    F    G    H    I                           __________________________________________________________________________     Ethyl acrylate                                                                            --   --   --    6.3 --    6.3 35.0  5.0  5.0                        Butyl acrylate                                                                            47.1 41.1 41.4 37.4 41.1 37.4 35.0 25.1 52.0                        Methoxyethyl acrylate                                                                     31.4 27.4 32.1 24.8 27.4 24.8 23.5 18.4 41.5                        Polyethylene glycol                                                                        .sup. 20.0*.sup.1                                                                   .sup. 30.0*.sup.1                                                                   .sup. 25.0*.sup.1                                                                   .sup. 30.0*.sup.1                                                                   .sup. 30.0*.sup.2                                                                   .sup. 30.0*.sup.2                                                                   .sup. 5.0*.sup.1                                                                    .sup. 5.0*.sup.1                                                                   --                          acrylate                                                                       Vinyl chloroacetate                                                                        1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5                        __________________________________________________________________________      *.sup.1 Methoxytriethylene glycol acrylate                                     *.sup.2 Ethoxydiethylene glycol acrylate                                 

Using the thus obtained acrylic copolymer elastomers, blends were prepared according to a blending recipe shown in Table 3.

                  TABLE 3                                                          ______________________________________                                         (Blending recipe)                                                                               (parts by weight)                                             ______________________________________                                         Acrylic copolymer elastomer                                                                       100                                                         Stearic acid       1                                                           MAF carbon         3                                                           Sodium stearate    3                                                           Potassium stearate 0.5                                                         Sulfur             0.25                                                        ______________________________________                                    

The blending was conducted in an open roll heated at 50° to 60° C. The obtained blends were press-vulcanized at 170° C. for 20 minutes, and further heat-treated in a gear oven at 170° C. for 4 hours. The resulting vulcanizates were measured for vulcanization characteristics according to JISK-6301. The results are shown in Table 4.

                                      TABLE 4                                      __________________________________________________________________________     (Vulcanization properties)                                                                      Ex. 1                                                                               Ex. 2                                                                               Ex. 3                                                                               Ex. 4                                                                               Ex. 5                                                                               Ex. 6                                                                               CEx. 1                                                                              CEx.                                                                                CEx. 3                Acrylic copolymer elastomer                                                                     A    B    C    D    E    F    G    H    I                     __________________________________________________________________________     Mooney viscosity of a copolymer                                                                 36   28   35   39   19   25   39   37   37                    (ML.sub.1+4, 100° C.)                                                   Mooney viscosity of a compound                                                                  55   54   56   56   45   47   52   59   50                    (ML.sub.1+4, 100° C.)                                                   Properties in normal conditions                                                Tensile strength (kg/cm.sup.2)                                                                  110  100  105  115  100  115  110  80   100                   Elongation (%)   190  170  180  175  170  190  230  150  190                   100% modulus (kg/cm.sup.2)                                                                      70   53   60   63   55   58   51   70   57                    Hardness (JIS-A) 67   65   64   69   63   64   66   73   66                    Heat resistance (175° C. × 168 hrs,                               degradation by air heating)                                                    Change in tensile strength (%)                                                                  -26  -20  -18  -15  -17  -20  -10  -30  -35                   Change in hardness (point)                                                                      +9   + 7  +8   +6   +10  +8   +3   +16  +7                    Oil resistance (JIS, #3 oil,                                                                    +26.5                                                                               +24.5                                                                               +23.7                                                                               +29.0                                                                               +27.9                                                                               +29.1                                                                               +22.0                                                                               +35.0                                                                               +28.3                 150 × 7 hrs.)                                                            Change in volume (%)                                                           Cold resistance  -37.2                                                                               -39.0                                                                               -37.5                                                                               -37.5                                                                               -38.8                                                                               -38.0                                                                               -25.0                                                                               -45.5                                                                               -32.0                 Impact brittleness test (°C.)                                           Compression set (%)                                                                             42   47   40   39   50   45   37   75   46                    (150° C. × 70 hrs)                                                __________________________________________________________________________      Ex.  Example                                                                   CEx.  Comparative Example                                                

EXAMPLES 7 TO 12 AND COMPARATIVE EXAMPLES 4 TO 6

Using the acrylic copolymer elastomers produced in the above Examples and Comparative Examples, blends were prepared according to a blending recipe shown in Table 5. In the same way as in said Examples and Comparative Examples, the heat treatment was conducted to form vulcanizates, and said vulcanizates were measured for properties. The results are shown in Table 6.

                  TABLE 5                                                          ______________________________________                                         (Blending recipe)                                                                               (parts by weight)                                             ______________________________________                                         Acrylic copolymer elastomer                                                                       100                                                         Stearic acid       1                                                           MAF carbon         60                                                          Zinc di-n-butyldithiocarbamate                                                                    1.5                                                         2,4,6-Trimercapto-s-triazine                                                                      0.5                                                         Diethylurea        0.3                                                         ______________________________________                                    

                                      TABLE 6                                      __________________________________________________________________________     (Vulcanization properties)                                                                      Ex. 7                                                                               Ex. 8                                                                               Ex. 9                                                                               Ex. 10                                                                              Ex. 11                                                                              Ex. 12                                                                              CEx. 4                                                                              CEx.                                                                                CEx. 6                Acrylic copolymer elastomer                                                                     A    B    C    D    E    F    G    H    I                     __________________________________________________________________________     Mooney viscosity of a copolymer                                                                 36   28   35   39   19   25   39   37   37                    (ML.sub.1+4, 100° C.)                                                   Mooney viscosity of a compound                                                                  53   53   52   52   50   49   48   56   48                    (ML.sub.1+4, 100° C.)                                                   Properties in normal conditions                                                Tensile strength (kg/cm.sup.2)                                                                  105  100  100  105  100  100  100  75   100                   Elongation (%)   170  160  170  165  150  170  180  160  170                   100% modulus (kg/cm.sup.2)                                                                      65   60   60   59   58   58   55   68   59                    Hardness (JIS-A) 69   67   66   66   64   65   63   68   67                    Heat resistance (175° C. × 168 hrs,                               degradation by air heating)                                                    Change in tensile strength (%)                                                                  -13  -15  -14  -12  -17  -18  -8   -27  -25                   Change in hardness (point)                                                                      +11  + 12 +13  +9   +11  +9   +8   +18  +8                    Oil resistance (JIS, #3 oil,                                                                    +25.3                                                                               +24.1                                                                               +22.9                                                                               +28.6                                                                               +28.2                                                                               +29.5                                                                               +21.2                                                                               +36.0                                                                               +27.3                 150 × 7 hrs.)                                                            Change in volume (%)                                                           Cold resistance  -37.2                                                                               -39.2                                                                               -38.0                                                                               -37.7                                                                               -38.8                                                                               -37.0                                                                               -23.0                                                                               -43.5                                                                               -32.4                 Impact brittleness test (°C.)                                           Compression set (%)                                                                             19   18   21   18   20   19   18   48   20                    (150° C. × 70 hrs)                                                __________________________________________________________________________      Ex.  Example                                                                   CEx.  Comparative Example                                                

EXAMPLES 13 TO 16 AND COMPARATIVE Examples 7 TO 9

Polymerization was performed as in the above Examples and Comparative Examples except that glycidyl methacrylate was used as the crosslinkable monomer as shown in Table 7. Polymerization conversion was 95 to 98%. Coagulation and recovery were carried out as in said Examples and Comparative Examples to obtain acrylic copolymer elastomers.

                                      TABLE 7                                      __________________________________________________________________________     (Monomer composition)                                                                     Acrylic copolymer                                                              elastomer                                                           Monomer composition                                                                       J    K    L    M    O    P    Q                                     __________________________________________________________________________     Ethyl acrylate                                                                            --    6.3 --    6.3 35.0  5.0  5.0                                  Butyl acrylate                                                                            47.1 37.4 41.1 37.4 35.0 25.1 52.0                                  Methoxyethyl acrylate                                                                     31.4 24.8 27.4 24.8 23.5 18.4 41.5                                  Polyethylene glycol                                                                        .sup. 20.0*.sup.1                                                                   .sup. 30.0*.sup.1                                                                   .sup. 30.0*.sup.2                                                                   .sup. 30.0*.sup.2                                                                   .sup. 5.0*.sup.1                                                                    .sup. 50.0*.sup.1                                                                  --                                    acrylate                                                                       Glycidyl methacrylate                                                                      1.5  1.5  1.5  1.5  1.5  1.5  1.5                                  __________________________________________________________________________      *.sup.1 Methoxytriethylene glycol acrylate                                     *.sup.2 Ethoxydiethylene glycol acrylate                                 

Using the obtained acrylic copolymer elastomers, blends were prepared according to a blending recipe shown in Table 8. In the same way as in the above Examples and Comparative Examples, the heat treatment was conducted to form vulcanizates, and said vulcanizates were measured of properties. The results are shown in Table 9.

                  TABLE 8                                                          ______________________________________                                         (Blending recipe)                                                                               (parts by weight)                                             ______________________________________                                         Acrylic copolymer elastomer                                                                       100                                                         Stearic acid       1                                                           MAF carbon         60                                                          Ammonium benzoate  1.5                                                         ______________________________________                                    

                                      TABLE 9                                      __________________________________________________________________________     (Vulcanization properties)                                                                      Ex. 13                                                                              Ex. 14                                                                              Ex. 15                                                                              Ex. 16                                                                              CEx. 7                                                                              CEx. 8                                                                              CEx. 9                          Acrylic copolymer elastomer                                                                     J    K    L    M    O    P    Q                               __________________________________________________________________________     Mooney viscosity of a copolymer                                                                 39   30   30   34   39   37   37                              (ML.sub.1+4, 100° C.)                                                   Mooney viscosity of a compound                                                                  65   64   62   64   52   59   50                              (ML.sub.1+4, 100° C.)                                                   Properties in normal conditions                                                Tensile strength (kg/cm.sup.2)                                                                  100  105  100  100  110  80   100                             Elongation (%)   180  180  190  175  230  150  190                             100% modulus (kg/cm.sup.2)                                                                      68   63   64   63   51   70   57                              Hardness (JIS-A) 69   68   67   65   66   73   66                              Heat resistance (175° C. × 168 hrs,                               degradation by air heating)                                                    Change in tensile strength (%)                                                                  -16  -15  -18  -17  -10  -30  -35                             Change in hardness (point)                                                                      +8   +7   +7   +8   +3   +16  +7                              Oil resistance (JIS, #3 oil,                                                                    +24.5                                                                               +25.8                                                                               +24.5                                                                               +27.6                                                                               + 22.0                                                                              +35.0                                                                               +28.3                           150 × 7 hrs.)                                                            Change in volume (%)                                                           Cold resistance  -38.2                                                                               -38.0                                                                               -37.5                                                                               -37.0                                                                               -25.0                                                                               -45.5                                                                               -32.0                           Impact brittleness test (°C.)                                           Compression set (%)                                                                             25   26   26   28   37   75   46                              (150° C. × 70 hrs)                                                __________________________________________________________________________      Ex.  Example                                                                   CEx.  Comparative Example                                                

EXAMPLES 17 TO 20 AND COMPARATIVE EXAMPLE 10

Using the acrylic copolymer elastomers J, K. L. M and Q prepared in the above Examples and Comparative Examples, blends were prepared according to a blending recipe shown in Table 10. Vulcanizates were formed under the same conditions as in said Examples and Comparative Examples, and measured for properties. The results are shown in Table 11.

                  TABLE 10                                                         ______________________________________                                         (Blending recipe)                                                                                  (parts by weight)                                          ______________________________________                                         Acrylic copolymer elastomer                                                                          100                                                      Stearic acid          1                                                        MAF carbon            60                                                       Isocyanuric acid      0.7                                                      Stearyltrimethylammonium bromide                                                                     1.8                                                      Diphenylurea          1.3                                                      ______________________________________                                    

                                      TABLE 11                                     __________________________________________________________________________     (Vulcanization properties)                                                                      Ex. 1                                                                               Ex. 2                                                                               Ex. 3                                                                               Ex. 4                                                                               Ex. 5                                     Acrylic copolymer elastomer                                                                     J    K    L    M    O                                         __________________________________________________________________________     Mooney viscosity of a copolymer                                                                 33   30   30   34   39                                        (ML.sub.1+4, 100° C.)                                                   Mooney viscosity of a compound                                                                  64   62   66   67   59                                        (ML.sub.1+4, 100° C.)                                                   Properties in normal conditions                                                Tensile strength (kg/cm.sup.2)                                                                  105  100  100  105  110                                       Elongation (%)   190  185  185  170  185                                       100% modulus (kg/cm.sup.2)                                                                      65   70   68   65   68                                        Hardness (JIS-A) 67   68   65   66   69                                        Heat resistance (175° C. × 168 hrs,                               degradation by air heating)                                                    Change in tensile strength (%)                                                                  -5   -6   -3   -6   -7                                        Change in hardness (point)                                                                      +9   +9   +8   +9   +8                                        Oil resistance (JIS, #3 oil,                                                                    +22.5                                                                               +23.6                                                                               +23.6                                                                               +24.8                                                                               +22.6                                     150 × 7 hrs.)                                                            Change in volume (%)                                                           Cold resistance  -37.2                                                                               -37.2                                                                               -37.1                                                                               -36.7                                                                               -32.1                                     Impact brittleness test (°C.)                                           Compression set (%)                                                                             17   18   15   18   17                                        (150° C. × 70 hrs)                                                __________________________________________________________________________      Ex.  Example                                                                   CEx.  Comparative Example                                                

From Tables 4, 6, 9 and 11, it follows that the vulcanizates of the acrylic copolymer elastomers in this invention are improved in cold resistance without impairing heat resistance, oil resistance and ozone resistance inherent in vulcanizates of acrylic polymers and are excellent in balance between oil resistance and cold resistance. 

What we claim is:
 1. An acrylate copolymer elastomer obtained by copolymerizing(a) 45 to 89.9% by weight of a monomer represented by the formula ##STR7## wherein R¹ denotes an alkyl group having 1 to 8 carbon atoms, and/or a monomer represented by the formula ##STR8## wherein R² denotes an alkylene group having 1 to 8 carbon atoms, and R³ denotes and alkyl group having 1 to 8 carbon atoms, (b) 10 to 45% by weight of a monomer represented by the formula ##STR9## wherein R⁴ denotes a hydrogen atom or a methyl group, R⁵ denotes a hydrocarbon group having 1 to 8 carbon atoms, m is an integer of 2 to 10, and n is an integer of 2 to 3, (c) 0.1 to 10% by weight of a crosslinkable monomer, and (d) 0 to 30% by weight of a monoethylenically unsaturated monomer copolymerizable with components (a), (b) and (c), said elastomer having Mooney viscosity [ML₁₊₄, 100° C.] of 10 to
 100. 2. An acrylic copolymer elastomer obtained by copolymerizing(a) 45 to 89.9% by weight of a monomer represented by the formula ##STR10## wherein R¹ denotes an alkyl group having 1 to 8 carbon atoms, and/or a monomer represented by the formula ##STR11## wherein R² denotes an alkylene group having 1 to 8 carbon atoms, and R³ denotes an alkyl group having 1 to 8 carbon atoms, (b) 10 to 35% by weight of monomer represented by the formula ##STR12## wherein R⁴ denotes a hydrogen atom or a methyl group, R⁵ denotes a hydrocarbon group having 1 to 8 carbon atoms, m is an integer of 2 to 10, and n is an integer of 2 to 3, (c) 0.1 to 10% by weight of a crosslinkable monomer, and (d) 0 to 30% by weight of a monoethylenically unsaturated monomer copolymerizable with components (a), (b) and (c), said elastomer having Mooney viscosity [ML₁₊₄, 100° C.] of 10 to
 100. 